High dispersion fluosilicate glasses



SePt- 13, 1949. KuAN-HAN SUN i 2,481,701

HIGH DISPERSION FLUOSILICATE GLASSES Filed Jan. 29, 1946 ATTORNEY Patented Sept. 13, 1949 UNITED STATES PATENT GFFICE 2,481,701 HIGH DISPERSION FLUOSILICATE GLASSES Kuan-Han Sun,

Eastman Kodak Company,

Rochester, N. Y., assignor to Rochester, N. Y., a.

corporation of New Jersey Application January 29, 1946, Serial No. 644,182

( Claims. (C1. G-52) of the same refractive indices, or lower refractive indices for the same dispersions or Abbe values. It is often desirable, from the optical point of view, to have glasses with even vhigher dispersions than the presently available flint glasses. It is an object of this invention to furnish such glasses which lalso lill the other requirements for optical glasses, such as transparency, reasonable weather resistance, the ability to take a high polish, and to withstand manufacturing operations.

This object is attained by the introduction into a silicate glass batch of relatively large amounts of fluoride. Fluor crown glasses have long been known, but the amount of fluoride present in them has been small, much less than the proportions here disclosed.

Reference will be made to the accompanying sheet of drawings wherein Figure l is a diagram showing the proportions useful in glass making, yand Figure 2 is a diagram showing the optical properties of the glasses.

In general, the composition of .the glasses may be represented'by the ternary system of the general formula AF-ROn-SiOz, where AF represents alkali metal fluoride, particularly NaF or KF or a mixture of them, and RO.. represents 'IiOzV or CbOzr. (usually as CbzOs) oria mixture of them. The proportions in which theseconstituents may be combined successfully to form very definitely cannot be combined in all proportions.

The approximate limits in which glass formation is attained is indicated in the following genla glass is found in practice to be limited. They v eral formulas, in which the ranges of the per4 n cent by weight and molal proportions are given:

APPROXIMATE LIMITS or GLAss FORMATION REGIONS System A.-NaF-Ti0z-Sz`02 Wt. per mol. per cent cent NaF 29-38 40-51 '11102 26-39 19-28 S10; 26-40 22-38 System B.-NaFCbO2.e-Si0z Wt. per mol. per cent cent System C'.-KF-TOs-Sz'0z Wt. per mol'. per cent cent KF 2533 2936 26-40 21-33 SiOz 30-46 33-48 It is to be noted that the molecular amount of potassium fluoride that can 'be introduced is materially less than of sodium liuoride. It is also to be noted that glass may be formed from a batch containing about 50y mol. per cent yof NaF. The atomic or ionic ratio of iiuorine to oxygen in such a formula is about 1:2'.

System A is particularly desirable from the point of' View of' optical properties. Figure 1 indicates for that system, in a ternary diagram, the limits of the region of glass formation, lboth in weight and mole per cent, by full and broken lines, respectively. The boundary lines indicated are empirical and do not indicate a sharply de'- i'lned boundary under all conditions, since glass formation is a function of experimental conditions such as the size of the melt, rate of cooli-ng, shape of the final glass piece, and -other operating conditions.. They represent the limits found experimentally by me with batches of 'the size and under the conditions described hereinafter. Analogous diagrams -could be shown for the other systemsr but Figure 1 is sufficient Ito show graphically how comparatively narrow are the operative limits of the proportions vwithin which the ingredients may be used under any given set of conditions. Other examples differing speciiically from those herein given are to be found in the co-pending application of E. F. Osborn and P. F. De Paolis, ySerial No. 722,276, filed January 15,

Specic examples will now be given within the ambit of the general formulas given above, W designating weight per cent, and M, mole per cent; and the values, Where known, of nD, the index of refraction of the D line, and of v, the Abbevalue, being. also given.

System A NaF TiOz SiOz Example No. D u

W M- W M W MV 1 34 45; l 27 18. 8 39 36. l l. 5961 32. 71 2. 33 44.1 29 20. 4 38 35. 5 1.614 3l l 3. 37 48. 9 3l 21'. 5 32 V29. 6 l. 608 30. 6 4.. 32 43. 2 32 22. 8 36 34.0 1.6255 29; 6 5.- 30 40. 9 32 22.9 38 36. 2 1.646 27.7 6.- 33. 3 44. 9 33. 3 23. 6 33.y 3 3l. 5 1. 638 28. 4 7.- 32 43. 5 34V 24. 3 34 32.2 l.. 638 28. 8 8.. 35 47. 0 35 24. 7 30 28. 3 1.645 27. 61 9.. 34` 46. 0 36 25. 6 30 28. 4 10. 38 50. 8 38 26. 7 24 22. 5 l. 6531 26'. 37 l1. 34 46. 2 38 27. 2 28 26. 6 l. 6686 29. 95 l2 31. 8 43. 2 33. 6 24. O 34. 6 32. 8 l. 6511 27. 8

System B Nar obo... sio. Example No. 11D v W M W M W M 39.0 35 17.3 4o 40.0 a9 19.7 as 39.6 43 22.4 33 45.5 44 22.6 2s 44.1 44 22.7 29 42.2 46 24.2 2s 43.8 48 25.6 26 42.9 o 27.1 25 45.0 52 28.4 22

As an example of the presence of both titanium and columbium oxides, the following example is given:

NaF T102 CbOM SiOz 'Example No.

' W M W M W M W M System C KF T104 Si02 Example No. I A ne v W M W M W M 31 34. 0 27 21. 5 42 44. 5 1. 605 26 28. 8 30 24. 1 44 47. l 32 35. 3 30 24. 1 38 40. 6 1. 663 27. 7 28 31. 1 32 26. 9 40 43. 0 l. 645 30 33. 6 35 28. 5 35 37. 9 1. 623 31. 1 26 V29.8 86 29.4 38 40.8 30 34. 0 39 32. 1 31 33. 9 1. 687 `25. 7

While the systems described above are described as purely ternary, it is to be understood that other ingredients usual in glass making may be added within the scope of the invention, An example of such a variation in system is given below:

EXAMPLE 30 Sodium iluoride (N aF) nn 1.6889 v 29.5

The partial dispersions of some of the glasses have been ascertained and are givenin the follow- Referring to the chart of Figure 2 in which the coordinates are 11D and u, the lines M and N indif cate the lower limit of refractive indices of the generally available int glasses and ofthe present glasses, respectively, these being calculated from the equations.

Vglass of over 96% silica. Such Points are indicated by the example numbers evident, they all fall within the band between the two lines and in general closer to the line N than to M, particularly those of System A (Examples 1 to 12). So far as I am aware, glasses have not hitherto been known having properties extending throughout this region. Y

In making these glasses, anhydrous powdered raw materials should be used. The batch may be mixed uniformly and introduced into a. covered platinum crucible or beaker. For a batch of 400 grams, coming within Systems A or B, heating at 11501200 C. for about one and one-half hours is sufficient to obtain a clear and uid liquid if stirred occasionally with a platinum stirrer. The melting temperature varies with the diiierent systems and particular compositions. With batches of System C, a temperature about 100 C. higher is necessary.

The greater the percentage of titanium or columbium oxide, the higher is the required ,temperature andthe longer thev time of Vmelting; and, conversely, higher percentages of alkali luorides lower both the time and temperature required. Since the uorides mentioned melt at a relatively low temperature (992 C. for NaF or 857 C. for KF) to a uid liquid, the titanium and columbium oxides tend to sink, and stirring is therefore necessary to facilitate complete solu- 280-460 C. It is then slowly cooled in the mold Y to room temperature. Y

There is a tendency for the glass containing titanium to Vhave a slightly yellowish tint. This has been found partly to be the case when melting of the batch takes place in a platinum vessel. This color can be nearly or completely eliminated if melting Vis performed in a vessel made of a a glass is described in the Journal of theAmerican Ceramic Society,

AOctober 1, 1944, pages 299-305 and is marketed under the trade-mark VYCOR..V This eliminates the initial action of the batch ingredients when they are most corrosive in their action on platinum. After solution,A the .batch may vbe poured into a platinum vessel. andvstirred and'may remain there before pouring into a mold as long as an hour without serious discoloration.

Having thus described my invention, what I claim is:

1. An optical glass in which 11D lies between 1.58 and 1.70, and v lies between 25 and 35, resulting from fusion of a batch comprising es-` sentially by weight alkali metal iluoride chosen from the group consisting of the iiuoride of sodium, the iiuoride of potassium, and a mixtureY of the fluorides of sodium and potassium, 22 to 38 per cent; oxide chosen from the group consisting of the oxideV of titanium, the oxide of rcolumbium, and a mixture of the oxides of tigroup consisting of the fluoride of sodium, the

fiuoride of potassium, and a mixture of the uorides of sodium and titanium oxide,V 26 to 40 per cent; silica, 26 to 46 per cent.

which 71D lies betweenV potassium, 25 to 38 per cent;V

3. An optical glass consisting of sodium fluoride, 29 to 38 per cent by weight; titanium oxide, 26 to 39 per cent; and silica, 26 to 40 per cent.

4. An optical glass resulting from fusion of a batch consisting of sodium fluoride, 22 to 28 per cent by Weight; columbium oxide, 32 to 54 per cent; and silica, 20 to 43 per cent.

5. An optical glass resulting from fusion of a 6 batch consisting of potassium uoride, 25 to 33 per cent by weight; titanium oxide, 26 to 40 per cent; and silica, 30 to 46 per cent.

6. A glass as described in claim 1 containing also tungsten oxide in an amount not over 10 per cent by Weight.

KUAN-HAN SUN.

No references cited. 

